1. Field of the Invention
The present invention relates to an apparatus for and method of producing semiconductor devices. More particularly, the invention is concerned with method and apparatus for producing semiconductor devices, wherein a multiplicity of semiconductor wafers held in a vertical posture are mounted on a boat and are placed in a reaction tube which is supplied from its front end with reaction gas so that the semiconductor wafers are processed with the reaction gas.
2. Description of the Related Art
FIG. 1 schematically illustrates a conventional apparatus for producing semiconductor devices. This apparatus, generally designated at a numeral 100, has a reaction tube 2 made of quartz and designed to receive a quartz boat 1. The boat 1 carries a multiplicity of semiconductor wafers W, W.sub.0 to be processed. These semiconductor wafers are held in vertical posture and arranged in parallel with their surfaces directed forward or backward. The reaction tube 2 is surrounded by a heater 3 which is capable of heating the semiconductor wafer W and W.sub.0 to a predetermined temperature. At the same time, a reaction gas supply control device 4 is provided on the front end of the reaction tube 2 so as to supply a reaction gas G into the reaction tube 2 at a controlled flow rate. The reaction gas G flows through the row of the semiconductor wafers in the reaction tube 2 so as to effect predetermined processing on the wafers W and is then discharged to the outside through a duct 5 provided on the rear end of the reaction tube 2.
A power supply controller 6 connected to the heater 3 is capable of controlling the electric current in the heater 3. A closure or lid provided on the rear end of the reaction tube closes the rear end opening of the reaction tube 2 through which the boat 1 is loaded into and removed from the reaction tube 2.
This apparatus 100 for producing semiconductor devices has an advantage that a multiplicity of semiconductor wafers W are processed at once. This apparatus, however, suffers from the following disadvantage. Namely, the reaction gas G, when it enters into the space indicated at A between the final wafer W.sub.0 of the wafer row and the lid 7 on the rear end of the reaction tube 2, a turbulency of flow of the reaction gas is generated as indicated at V because the volume or the cross-sectional area of the flow passage drastically increases. Such a turbulency of reaction gas may cause the ambient air to be induced into the reaction tube 2 through the gas outlet port (not shown) provided in the lid 7. The air may reach the rear end of the row of the wafers across the above-mentioned space A. In consequence, the ambient air, particularly oxygen contained in the air, is undesirably trapped in the semiconductor wafer or wafers, with the result that characteristics of the product semiconductor device are seriously impaired and reduce the yield.
For the purpose of eliminating such a problem, it would be an effective measure to increase the length of the space A, i.e., to increase the distance between the final wafer W.sub.0 and the lid 7 so as to keep the final wafer W.sub.0 from any unfavorable effect which may be caused by air induced as a result of turbulency of flow of the reaction gas. Such a measure, however, is disadvantageous in that the number of the semiconductor wafer W which can be processed in a reaction tube of a given length is decreased so that the production efficiency is lowered undesirably. In order to achieve a high production efficiency while avoiding the above-described problems of the prior art, it is necessary to employ a reaction tube 2 having a large length, with the result that the overall length of the apparatus is undesirably increased.